Charge control system to reduce risk of an aircraft-initiated lightning strike

ABSTRACT

System for reducing likelihood of an aircraft-induced lightning strike on an aircraft. The system includes a plurality of electric field sensors distributed on surfaces of the aircraft to monitor continuously the electrical environment to which the aircraft is subjected. A plurality of ion emission sources are distributed on selected aircraft surfaces, the ion emission sources adapted to emit either positive or negative ions. A computer runs an algorithm to control net charge level of the aircraft by commanding the emission of positive or negative ions from selected surfaces to retard inception of corresponding leader discharges.

This application claims priority to U.S. Provisional Application Ser.No. 62/330,305 filed on May 2, 2016, the content of which isincorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

This invention relates to aircraft protection, and more particularly, toa charge control system to reduce the risk of a lightning strike on anaircraft.

On average, a civil air is struck by lightning at least once per year.The probability of an aircraft being struck while airborne is muchhigher than that of a stationary aircraft on a runway. Part of thereason is that the aircraft modifies the electric fields in the vicinitywhich acts as a catalyst for lightning inception and attachment.Specifically, an aircraft located in an electric field becomes polarizedand the local electric field values at the aircraft surface aremagnified at the extremities where the radius of curvature of theconducting structure is smaller, such as on wing tips, stabilizer tipsaircraft nose, etc. The foregoing applies to both fully metallicaircraft and aircraft with a substantial past of their structuralmaterial made of composites so long as copper mesh or expanded foil isembedded in the structural material to ensure high electricalconductivity. This electric field enhancement can result in thedevelopment of a bi-directional leader extending from opposite polarityaircraft extremities, which may eventually connect with oppositelycharged regions in a cloud or ground. Through this process, the aircrafttriggers a lightning strike with itself being in the direct path of thereturn stroke current flowing between the attachment locations. See,FIG. 1 that shows the sequential limitation of a positive leaderfollowed by a negative leader in a sufficiently high electric field.

It is an object of the present invention to provide a system forminimizing the likelihood that leaders will form that can result in alightning strike.

SUMMARY OF THE INVENTION

The system disclosed herein for reducing likelihood of anaircraft-induced lightning strike on an aircraft in a region of highambient electric field includes a plurality of electric field sensorsdistributed on surfaces of the aircraft to monitor continuously theelectrical environment to which the aircraft is subjected. A pluralityof ion emission sources are distributed on selected surfaces of theaircraft, the ion emission sources adapted to emit either positive ornegative ions as required. A computer, preferably located in theaircraft, runs a series of algorithms to retrieve the ambient electricfield and aircraft net charge from the measurements of the electricfield sensors; to evaluate the safety margins for positive and negativeleader formation; and to control the net charge level of the aircraft bycommanding the emission of positive or negative ions at the selectedsurfaces to retard inception of corresponding leader discharges.

In a preferred embodiment, the electric field sensors are positioned sothat one of the 3 spatial components of the external field or the netcharge dominate in at least one sensor. In a preferred embodiment, aminimum of 4 electric field sensors are used. In a preferred embodiment,the ion emitters are located at the downstream extremities of theairplane which include antennas and VHF blades, trailing edges of wingtips, trailing edges of vertical and horizontal stabilizer tips, andtail cone. In a preferred embodiment, if conditions are such that apositive leader is likely to occur, one or several ion emission sourcesemit positive ions at one or several selected surfaces. In contrast, ifconditions are such that a negative leader is likely to occur, one orseveral ion emission sources emit negative ions at one or severalselected surfaces. In a preferred embodiment, the electric field sensorsare electric field mills. In a preferred embodiment, the ion emissionsources are high-voltage stinger probes, with the high voltage terminalof an onboard power supply ending in a corona discharge exposed to thewind and the low voltage terminal connected to the aircraft frame;electrospray sources; or ionic liquid ion sources forming a compactarray.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a schematic illustration showing the typical sequentiallimitation of positive and negative leaders when an airplane fliesthrough an electric field that triggers lightning.

FIG. 2 is a schematic view of an airplane showing representativelocations of electric field sensors and ion emission sources distributedon the airplane.

DESCRIPTION OF THE PREFERRED EMBODIMENT

It is generally accepted that the majority of lightning strikes toaircraft are triggered by the aircraft itself [Larsson2002] as itpenetrates a region of high ambient electric field or is subjected to arapid rise in the electric field to which it is exposed. According to[Lalande1999] the critical ambient field leading to lightning initiationranges from 90 kV/m to 300 kV/m (calculated fields at mean sea levelconditions), for a narrow body commercial airplane.

In this sense, lightning would most likely not have happened in theabsence of the aircraft. This is the case because as a conductiveaircraft penetrates a region of high electric field, it becomespolarized, with one end becoming positively charged and the other endbecoming negatively charged, even under zero net charge conditions. Thiseffect significantly enhances the electric field on the aircraft'ssurface and its vicinity. For example, the presence of a convex metallicobject intensifies the electric field on its surface by factors thatrange from 2 (for a cylinder) or 3 (for a sphere) to something of theorder of l/d for an elongated object of length l and diameter d. Thisfield intensification is due to the accumulation of charge at theobject's ends as required to counter the external field on the aircraft.For an aircraft flying below the clouds, most of the time, a cloud baseis negative with respect to ground so a positive (upwards) field Edevelops. In this scenario, convex surfaces on the aircraft (e.g. anairplane) that face upwards, such as the tip of the empennage or the topof the fuselage, accumulate positive surface charge in response, whilesurfaces facing down accumulate negative surface charge in the sameamount (for an uncharged aircraft). For an aircraft flying close to theclouds, the ambient electric field E can take any orientation. In thisscenario, still one side of the aircraft will accumulate positive chargeand the other negative charge, the summation of these charges amountingto the net charge of the aircraft (zero in the case of an unchargedaircraft). In general, the polarity of different strikes of the aircraftand their charge level depend on the orientation and amplitude of theexternal field, as well as the net charge of the aircraft.

As the electric fields on the aircraft's surface and its vicinityintensify, localized streamer corona discharges can develop and, iffurther stressed, the streamers may coalesce into self-propagatingleader channels. In general, two leaders of opposite polarity form fromthe aircraft prior to the lightning strike. However, once the firstleader forms, formation of the second leader is imminent and occursseveral milliseconds later as propagation of the first leader biases theelectric potential of the aircraft in the direction that favors theformation of the leader of opposite polarity. The discharge is nowbi-directional, and both branches propagate until they connect withground and cloud, or sometimes with two clouds of opposite polarity,thus initiating the destructive first return stroke of a lightning arc.Other strokes may then follow along the same channel.

There is a definite order to this process because the crucial breakdownfield in air is known to be around twice as large on the negative sideas compared to the positive side, and the conditions for negative leaderformation are generally more demanding than for the positive leader.Therefore, under most circumstances, a positive leader typicallydevelops first which drains positive charge from the aircraft and shiftsits potential in the negative direction, until the conditions at thenegative end are sufficient to initiate a sell-propagating negativeleader a few milliseconds later (FIG. 1).

The charge control system described in this invention exploits thisasymmetry between the positive and the negative leader inception toreduce the risk of an aircraft-initiated lightning strike. The systemacts to suppress the inception of the first leader while ensuring that aleader of opposite polarity does not form.

In a preferred embodiment, the charge control system to reduce risk ofan aircraft-initiated lightning strike (FIG. 2) consists of electricfield sensors 12, a series of algorithms run on the computer 16preferably carried on the aircraft 10, and ion emitters 14. The purposeand details of each of these elements are described in what follows.

With reference now to FIG. 2 an aircraft 10 has distributed on itssurface onboard electric field, sensors 12 indicated by rectangles onthe figure. In the figure, the arrows indicate the electric fieldsensors' orientations. At least four electric field sensors are requiredto be able to determine the 3 spatial components of the external vectorelectric field plus the net aircraft charge from the electric fieldsmeasured by the sensors. However, at, least six sensors are preened forbetter accuracy. Proper location of the electric field sensors isrequired to unambiguously determine the external field and net aircraftcharge. Preferred placement of the electric field sensors 12 requiresthat each of the 3 spatial components of the external field, relative toan aircraft reference frame, or the net charge dominate in at least onesensor. An example placement of the electric field sensors in anairplane is shown in FIG. 2, as recommended by [Mach2007]. Otherpreferred placements for airplanes include the wing tips, bellycenterline near the nose and near the tail [Anderson1984]. The 3 spatialcomponents of the external field (E_(x), E_(y), E_(z)) as well as theaircraft net charge Q (or equivalently its electric potential) will beretrieved from the electric fields measured locally by the sensors 12using an algorithm run on the computer 16 preferably carried on theaircraft 10. The algorithm continuously retrieves the external electricfield and aircraft net charge from a previously calibrated matrix (whichdepends on the aircraft geometry and the location of the sensors 12) andthe individual instrument responses. Possible algorithms and calibrationprocedures have been reported in the literature [Mach2007, Winn1993,Koshak2006], Suitable electric field sensors are rotating shutter fieldmeters, called electric field mills or which are described elsewhere[Winn1993].

From the inferred instantaneous external field and aircraft net charge,another algorithm run on the computer 16 preferably carded on theaircraft 10 will determine the likelihood of positive and negativeleader inception from corresponding select aircraft surfaces. Thesesurfaces should at least include: the aircraft nose, antennas and VHFblades, leading and trailing edges of wing tips, vertical and horizontalstabilizer tips, tail cone, and engine nacelles. The algorithm willdetermine the probability of leader inception of either polarity basedon best-known literature methods [Lalande1999, Zaglauer1999]. Note thatthe inception thresholds for either polarity are different and it isprecisely this asymmetry that is exploited. E.g., a possible leaderinception model is based on a critical equivalent charge concept: if thecalculated corona charge exceeds a certain threshold, a leader isincepted [Gallimberti1979, Cooray2014]. Experimental results[Castellani1998] show that an equivalent critical charge for thenegative leader is approximately 4 times higher than for the positiveleader (in magnitude). Critical electric fields necessary for thepropagation of streamer discharges that precede leader formation arearound two times higher for the negative polarity than for the positivepolarity.

From this information, yet another algorithm (the charge controlalgorithm) run on the computer 16 preferably carried on the aircraft 10calculates the optimum net charge of the aircraft required to keep equalsafety margins for the positive and negative discharges, therebyreducing the likelihood of a lightning strike. Depending on thepredicted optimum net charge level, the ion emitters 14 are activated toforce this optimum charge condition. As an example, suppose that thealgorithm just described indicates that there is an X % safety marginfor the positive discharge (i.e. an increase of X % in the ambient fieldwould to a positive leader from the positive end of the aircraft) and a3X % safety margin for the negative discharge (i.e., an increase of 3X %in the ambient field would trigger a negative leader from the negativeend of the aircraft). In this situation, the ion emitters 14, shown bycircles. In FIG. 2, are activated to emit positive charge from one orseveral of the ion emitters 14 located on the positive region of theaircraft. As a consequence of the positive charge emission, the aircraftacquires negative charge and the negative side of the aircraft will seeits negative field intensified. The positive ion emission processcontinues until the algorithm indicates equal safety margins, Y %, forboth the positive and negative leaders. Necessarily Y is greater than Xand smaller than 3X, due to the asymmetry of the leaders, thus reducingthe likelihood of a lightning strike.

It should be appreciated that the strategy set out above is based on thelack of symmetry in the inception of the two leaders as shown in FIG. 1.Of course, there can be situations where the negatively polarized areapresents more pointed protuberances, or there is excess negative netcharge on the aircraft so that negative and positive leaders are equallylikely. In that case, the algorithm will predict that the optimum netcharge coincides with the actual aircraft net charge level, and the ionemitters 14 will not be activated since any ion emission would beundesirable. But in the opposite limit, with negative leader inceptionbeing actually more likely, the algorithm would predict an optimumcharge level greater than the actual one. In this situation, the ionemitters 14 will be activated to inject negative ions from thoseemitters located at the negative side of the aircraft, so that the netcharge of the aircraft becomes more positive. More generally, theoptimum level of aircraft charging is that which makes both polarityleaders equally unlikely. Assuming proper electric field sensorinstrumentation, this level can be continuously tracked. Incidentally,this strategy would be of use even in the absence of storm fieldsbecause aircraft can become charged, of either polarity, for otherreasons such as flight through dust or ice particle fields. Preexistingpositive charge is particularly damaging if the aircraft then flies intoa storm area.

Regarding requirements on the emitters, the optimum net charge levelsfor a business jet size airplane are estimated on the order 0.1-0.5 mCfor a wide range of conditions (typically of negative polarity). Atypical airliner flies about 250 m in one second and this may be of theorder of the motion required to enter the area of influence of a cloudcharge center. If a one second ion-evacuation time is assumed, the ioncurrent required is 100-500 μA. Moreover, if the potential bias for ionemission is of the order of 1 kV, the required power is of the order of0.1-0.5 W. Faster ion-evacuation times may be needed to counter fastraises in the ambient electric field, and in this situation higher ioncurrents will be required. A higher current can be achieved byactivating a larger number of ion emitters 14 or by increasing thecurrent level of each individual emitter.

With reference to FIG. 2 an aircraft 10 has distributed on its surfaceon-board ion emitters 14 indicated by circles on the figure. Ionemitters should be placed in pairs. A pair constitutes a positive ionemitter and a negative ion emitter. For some preferred embodiments asingle ion emitter able to operate in both polarities should be used ateach location. Ion emitters 14 are preferentially placed at thedownstream extremities of the aircraft which can include but are notlimited to: antennas and VHF blades, trailing edges of wing tips,trailing edges of vertical and horizontal stabilizer tips, and tailcone. These locations are selected to facilitate the convection of theemitted ions away from the aircraft by the airflow.

The charge control algorithm run on the computer 16 preferably carriedon the aircraft 10 will activate those ion emitters 14 located on thepositive side of the aircraft, if positive ion emission is required; oralternatively, on the negative side of the aircraft, if negative ionemission is required. E.g. in the case of positive ion emission, sincethe adjacent surface is positively biased, the ions will be immediatelysubjected to threes that pull them farther away from the aircraft. Thisrepulsion forces combined to the sweeping of the airflow will reduce thepossibility of ion return to the aircraft and thus facilitate the ionevacuation process. In general, reaching a required optimum net chargelevel in a given time can be adjusted through the number of ion emittersactivated at each time or through the individual current levels of eachof the emitters 14.

Suitable ion emitters to artificially charge an aircraft arehigh-voltage stinger probes producing coronas [Koshak2006, Vonnegut1961,Jones1990] and electrospray sources [FernandezMora2007], including ionicliquid ion sources [Perez2011].

The high-voltage stinger probe ion emitters require an onboard highvoltage power supply (of the order of 1-10 kV) with the high voltageterminal connected to a cable which terminates in a point or brush thatproduces a corona discharge exposed to the airstream. The low voltageterminal is connected to the airframe [Jones1990]. The polarity of thehigh voltage is positive for positive ion emission and negative fornegative ion emission. The currents emitted by each on of these emittersare of the order of 10 μA but can be increased through the geometry ofthe exposed electrode, the number of filaments in the brush or the levelof voltage applied.

Ion emitters based on electrospray principles rely on the emission ofcharged particles: either charged droplets (colloid), pure ions or amixture of both from the apex of an electrified liquid[FernandezMora2007]. In particular, ionic liquid ion sources [Perez2011]can emit ions of either positive or negative value with currents up to 1μA. In order to increase the current to usable levels, the emitters canbe multiplexed in the form of arrays. E.g. small ionic liquidmicro-arrays made at the Massachusetts Institute of Technology can emitabout 150 μA each with a unit area of about 1 cm², and this can beaccomplished using a 1 kV bias [Citierra2016]. Note that these emittersin particular are designed for vacuum operation and equivalent sourceswould need to be developed for atmospheric operation. Both polarities ofions can be emitted with essentially similar bias levels. It is worthnoting that the ion creation process for these sources does not involvecreating of a plasma that could possibly enhance surface breakdown;instead, ions are directly extracted from an ionic liquid and are notthemselves ionization sources for the ambient air.

The content of all of the references cited herein is incorporated byreference.

It is recognized that modifications and variations of the presentinvention will be apparent to those of ordinary skill in the art, and itis intended that all such modifications and variations be includedwithin the scope of the appended claims.

REFERENCES

-   [Mach2007] Mach M, Koshak W J. General matrix inversion technique    for the calibration of electric field sensor arrays on aircraft    platforms. Journal of atmospheric and oceanic technology 24 pp.    1576-1587, 2007-   [Winn1993] Winn W P. Aircraft measurement of electric field:    self-calibration journal of geophysical research 98(D4) pp.    7351.3365, 1993-   [Koshak2006] Koshak W J. Retrieving storm electric fields from    aircraft field mill data. Part I: Theory. Journal of atmospheric and    oceanic technology 23 pp. 1289-1302, 2006-   [Anderson1987] Anderson R V, Bailey J C. Vector electric fields    measured in a lightning environment, NRL Memorandum Report 5899,    1987-   [Lalande1999] Lalande P, Bondiou-Clergerie, Laroche P, Computations    of the initial discharge initiation zones on aircraft or helicopter.    SAE Technical paper series 1999-01-2371 reprinted from Proceedings    of the 1999 International Conference on Lightning and Static    Electricity (ICOLSE), 1999-   [Zaglauer1999] Zaglauer H W, Wulbrand W. A simplified model for the    determination of initial attachment zones via electric field    modeling—parameter studies and comparisons, SAE Technical paper    series 1999-01-2375, reprinted from Proceedings of the 1999    International Conference on Lightning and Static Electricity    (ICOLSE), 1999-   [Gallimberti1979] Gallimberti I. The mechanism of the long spark    formation. Journal de Physique Colloques 40 (C7) p C7-193-C7-259,    1979-   [Cooray2014] Cooray V. The Lightning flash, 2^(nd) edition, IET    power and Energy series 69, 2014-   [Castellani1998] Castellani A, Bondiou-Clergerie A, Lalande P,    Bonamy A, Gallimberti I. Laboratory study of the bi-leader process    from an electrically floating conductor, Part 2: bi-leader    properties, IEE Proc. Sci. Meas. Technol. 145 (5) pp. 193-199, 1998-   [Jones1990] Jones J. J. Electric charge acquired by airplanes    penetrating thunderstorms, Journal of geophysical research 95(D10)    pp. 16589-16600, 1990-   [Vonnegut1961] Vonnegut B, Moore B C, Mallahan F J. Adjustable    potential-gradient-measuring apparatus for airplane use. Journal of    geophysical research 66 pp. 2393-2397, 1961-   [FernandezMora2007] Fernandez de la Mora J. The fluid dynamics of    Taylor cones, J. Fluid Mech. 39 217-43, 2007-   [Perez2011] Perez-Martinez C, Guilet S, Gierak J, Lozano P. Ionic    liquid ion sources as a unique and versatile option in FIB    applications. Microelectronic Engineering, 88(8) pp. 2088-2091, 2011-   [Guerra2016] Guerra-Garcia C, Krejci D, Lozano P. Spatial unitbrmity    of the current emitted by an array of passively fed electrospray    porous emitters, J. Phys. D: Appl. Phys. 49 115503 (12 pp), 2016-   [Larsson2002] Larsson A. The interaction between a lightning flash    and an aircraft in flight. C. R. Physique 3 pp. 1423-1444, 2002

What is claimed is:
 1. A system for reducing likelihood of anaircraft-induced lightning strike on an aircraft in an atmosphere ofhigh ambient electric field comprising: a plurality of electric fieldsensors distributed on surfaces of the aircraft to monitor theelectrical environment to which the aircraft is subjected; a pluralityof ion emission sources distributed on one or more of the surfaces ofthe aircraft, the plurality of ion emission sources configured to emitpositive and/or negative ions; a computer configured to retrieve anexternal electric field and aircraft net charge from the plurality ofelectric field sensors; the computer also configured to evaluate asafety margin for positive and negative leader inception from the one ormore surfaces of the aircraft based at least partly on the retrievedexternal electric field and aircraft net charge; and the computer alsoconfigured to control the aircraft net charge by commanding the emissionof positive and/or negative ions from the plurality of ion emissionssources to retard inception of positive and/or negative leaderdischarges.
 2. The system of claim 1, wherein the one or more of thesurfaces include at least one selected from the group of trailing edgesof wingtips, trailing edges of tips of vertical and horizontalstabilizers, antennas and VHF blades, and a tail cone.
 3. The system ofclaim 1, wherein the plurality of electric field sensors is at leastfour electric field sensors.
 4. The system of claim 1, wherein theplurality of electric field sensors are located so that each of threecomponents of the external electric field or the aircraft net chargedominates in at least one of the plurality of electric field sensors. 5.The system of claim 1, wherein the safety margin of positive andnegative leader inception is evaluated at the surfaces which include theaircraft nose, antennas and VHF blades, leading and trailing edges ofwing tips, vertical and horizontal stabilizer tips, tail cone, andengine nacelles.
 6. The system of claim 1, wherein the computer isconfigured to command the emission of positive ions from one or more ofthe plurality of ion emissions sources before a positive leaderinception threshold is reached.
 7. The system of claim 1, wherein thecomputer is configured to command the emission of negative ions from oneor more of the plurality of ion emissions sources before a negativeleader inception threshold is reached.
 8. The system of claim 1, whereinthe computer is configured to command the emission of positive ornegative ions from one or more of the ion emissions sources to adjustthe aircraft net charge level so that inception of a positive and anegative leader have an equal probability.
 9. The system of claim 1,wherein if a positive leader is more likely to occur than a negativeleader, the computer is configured to command one or more of theplurality of ion emission sources to emit positive ions at one or moreof the surfaces.
 10. The system of claim 1, wherein if a negative leaderis more likely to occur than a positive one, the computer is configuredto command one or more of the ion emission sources to emit negative ionsat one or more of the surfaces.
 11. The system of claim 1, wherein thecomputer is configured to adjust a rate of aircraft net chargeaccumulation by adjusting a number of the plurality of ion emissionsources that are activated.
 12. The system of claim 1, wherein thecomputer is configured to adjust a rate of aircraft net chargeaccumulation by adjusting a current of each individual ion emitter. 13.The system of claim 1, wherein the computer is configured to command theemission of positive ions on positively charged surfaces of theaircraft.
 14. The system of claim 1, wherein the computer is configuredto command the emission of negative ions on negatively charged surfacesof the aircraft.
 15. The system of claim 1, wherein the electric fieldsensors are electric field mills.
 16. The system of claim 1, wherein theion emission sources are mounted in pairs: a positive ion emitter and anegative ion emitter.
 17. The system of claim 1, wherein the ionemission sources are configured to operate in both positive and negativepolarity.
 18. The system of claim 1, wherein the ion emission sourcesare ionic liquid ion sources.
 19. The system of claim 1, wherein the ionemission sources are ionic liquid micro-arrays.
 20. The system of claim1, wherein the ion emission sources are electrospray sources.
 21. Thesystem of claim 1, wherein the ion emission sources are high voltagestinger probes based on corona emission.
 22. The system of claim 1,wherein the ion emission sources are substituted by charged droplet orcolloidal emission sources.
 23. The system of claim 1, wherein the ionemission sources emit a combination of pure ions and charged droplets.24. The system of claim 1, wherein the computer is carried on theaircraft.
 25. The system of claim 1, wherein the computer is not carriedon the aircraft, and wherein the computer is configured to communicatewith the aircraft.
 26. The system of claim 1, wherein the aircraft is anairplane.
 27. The system of claim 1, wherein the aircraft is ahelicopter.
 28. The system of claim 1, wherein the aircraft is a drone.29. The system of claim 1, wherein the aircraft is any type ofconductive airborne vehicle.
 30. The system of claim 1, wherein thecomputer is configured to command one or more of the plurality of ionemissions sources located on a positive polarity surface to emitpositive ions, and wherein the computer is further configured tosimultaneously command one or more of the plurality of ion emissionssources located on a negative polarity surface to emit negative ions.31. A system for reducing likelihood of an aircraft-induced lightningstrike on an aircraft in an atmosphere of high ambient electric fieldcomprising: a plurality of electric field sensors distributed on aplurality of surfaces of the aircraft to measure a local electric fieldat each one of the plurality of surfaces; a plurality of ion emissionsources distributed on the plurality of surfaces of the aircraft,wherein the plurality of ion emission sources are configured to emitpositive and/or negative ions; and a computing device which receives thelocal electric field measurements from each of the electric fieldsensors, wherein the computing device is configured to: determine a netcharge of the aircraft based on the local electric field measurements;determine a probability of positive and/or negative leader inceptionfrom the plurality of surfaces based at least partly on the measuredlocal electric field and the net charge of the aircraft; and command oneor more of the plurality of ion emission sources to emit ions to reducethe probability of positive and/or negative leader inception based onthe determined probability.
 32. The system of claim 31, wherein thecomputing device is configured to determine a polarity of each one ofthe plurality of surfaces based on the local electric fieldmeasurements.
 33. The system of claim 32, wherein the computing deviceis configured to command ion emissions sources located on a positivepolarity surface to emit positive ions, and wherein the computing deviceis further configured to simultaneously command ion emissions sourceslocated on a negative polarity surface to emit negative ions.
 34. Amethod for reducing likelihood of an aircraft-induced lightning strikeon an aircraft in an atmosphere of high ambient electric field, themethod comprising: measuring a local electric field at a plurality ofsurfaces of the aircraft; determining a net charge of the aircraft basedon the local electric field measurements; determining a probability ofpositive and/or negative leader inception from the plurality of surfacesbased at least partly on the measured local electric fields and the netcharge of the aircraft; and emitting ions to reduce the probability ofpositive and/or negative leader inception based on the determinedprobability.